Electron discharge apparatus



' I f 161,6702' Feb. 8, 1927. M. MOR SON 7 ELECTRON DISCHARGE APPARATUS Filed Jan. l2, 1924 Patented F b. 8,1927,

MONTFORD MORRISON, or cIiIcAeo, ILLINoIs.

ELECTRON DISCHARGE nrrnnarusi Application filed January 12, 1924. Serial No. 685,301.

. My present invention relates to deviceswhich operate with the assistance of incandescent cathodes and has particular reference to such devices where the discharge produced is subject to variations in behavior due to changes in gas ionization within the device's, dIfferences 1n specific electron emissivity and instability of spontaneous electron liberation. 1

Among the objectsof my inventionare: first, to provide means vi'or stabilizing the electron discharge of theapparatusgwhen the source of electric current for heating the aforesaid incandescent cathodes is I subject to variation; second, to provide an improved constancy of conductivity'within the device when the said device is subject to gas 1onization; third, to provide an improved constancy oif-the electrioconductivity in the de vice when the specific emissivity of the incandescent cathodesis subject to variation; fourth, to provide an improved constancy of conductivity of the device when spontaneous ionizationmay be present or subject to variation. I

Other and further objects will be in part pointed out and in part obvious upon read ing the specifications and inspecting the drawing, but the novel scopeof my invention will be pointed out with certain particularities in the appended claims. For a clear nnderstandlng of my invenvtion reference may be had to thelfollowing description bearing, connection with theac-' companying drawing in which the figure is I j arevar'iations in the'temperatureof the oath I ode, variations in the specific electron emis sivity of the hot cathode itself, variations in a general and diagrammatic viewof one embodiment of my invention,

It is admitted that the art of controlling electron discharge apparatus by means subject to the discharge current through the tube is not new. Such apparatus has been in extensive use in connection with discharge tubes operating with pure gas ionization and in those in which only non-gas ionization is alleged to occur. In thermionic fX-ray tubes such devices have been depended upon principally to eliminate variations in the ex? citing current of the cathode filaments caused by supply-line voltage-fluctuations.

however, is not for the elimination of line variation-in exciting-current of the filament of an X-ray tube but the elimination of erratic behavior in x-m tubes employing The most important use" of my device,

hot cathodes. Although these tubes are alleged to be independent ofgas ionization,

experience in the art shows that there is an appreciable amount of gas nearly always present and thatfthe' actual pressure of this gas can varyfrom instant to instant. .There may be produced considerable gasionization at times and sufiicient toinjure the tube 7 not promptly taken care of,when it occurs in over-abundance. The elfectof this gas Ionization is to increase the conductlvity of the tube, that is, with a constant "filament; temperature the conductivity may rise or lower of its own accord. v

V The objects, of stabilizers ofthe priorv art I for electron dischargetubes have been par- I ticularlywdirected toward "the stabilization of X-ray tubes whenthe operation is supposed to take place independently of gaseous ion: ization, and their principal objects have been to provide'means for automaticallyregulating the electron emission, particularly when the source of heating-current for the incandescent" cathode varies in voltage due in-t 7 herently "to line fluctuations and it was thought that this was the principal source of.

operative erraticalness in these tubes; However, I have discovered that there are four sources of variation in the electrical conductivity of these tubes and that the principal difiiculty does'not originate from a variation in filament excitation voltage, but fromvariation 1n the aggregate electron emission from the four sources.

The four sources which I have discovered" the gas pressure'within the, tube which not only atlect' the gaseous ionization but also,

the electron emission ofthe filament itself,

as well as does it even change the spectrum of the targetdue to interference with the velocity-distribution of the electron stream,

and also variations in'spontaneous ionization which IS the pulling out of electrons themselves from parts of the cathode on whichlth'e electrostatic stresses are concen trat'ed, due to points, sharpfedges and the like.v s

It will be appreciated by those familiar with the art that in View of this explanation,

it is erroneous to assume that the stabiliza tion otany oneof these phenomena will af- 2 feet stabilization of the discharge current through the tube itself; and further, that if the discharge current is to be stabilized the aggregate electron liberation must be made constant as a whole and this may-be done by selecting one of the predominating factors of the aforementioned group which may be controlled external 0f the tube and construct a device Which will add to or subtract from the value of this selected factor in such a Wayas to maintain the aggregate at a substantially constant value.

Means. and methods for doing this are the substance 'of this invention.

Tn'all the devices of prior art, somesort of -a'relay hasbeen used to accomplish their result. In the-first case on record, a simple relay element in which the armature is actuated by the discharge current through the tube is madeto operate an osmosis regulator which lowers or raises the conductivity ofthesaid tube. In other developments of the relay element above decribed instead of being actuated by intermittent currents is made to vibrate synchronously With the alternation of the line voltageand this vibrating "action being utilized to accomplish stabilization of the discharge current.

'Inmy device I eliminate all'vibrating and relay parts such a 'usedin connection with H the case ofthe'vibrating armature which is supposed to operatesynchronously with the line voltage. The performance imposed uponthis instrument andthe'limits of variations'in its behaviorresult in thi being almost impractical as an operative device and'its' use in the art has for this reason been largely abandoned.

In'the'presentinvention '1 employ a special circuit for the excitation of the hot cathode of the electron discharge tube, such that aggregate electron liberation in the said tube ismaintained substantially constant'by the discharge-limitation "character istics of the circuits involved.

Referring to the figure, 1 is a source of alternating potential whichthrough leads 2 and 3 supp'lythe primary eof'the'stepup transformer 5.-with electrical energy. This described circuit may have a means 6,

I .of varying the "induction within the core of the said tran'sformer, and said circuit may be'fsupp'lied with a switch 7, for practical purposes.

"The aforesaid variations in the induction -of the COISlJIZLHSfOl'DlQI 5 produce different potentials in secondary '8 of said transformer. v i 7 High potential leads 9-and 1O conduct current to the alternating current terminals 11 and 12, of the rectifier 13, preferably :of

the kind set forth in my United States Letters P-atent'1,466,541, and lat-and 15 are the direct current terminals of said rectifier; the terminal '14 conducting current by means of lead 16 to the anode terminal 17 of the X-ray tube 18, preferably enclosed within the shield 19, as set forth inmy application Serial Number 633,712, filed April 21,1923.

h Direct current terminal 15, by means of lead 20, conducts negative potential to my stabilizing apparatus, as will be more fully hereinafter described.

Rectifier 13 is driven synchronously with the source of alternating potential 1, by mechanical connection, or by e'lectrical means,

The function of the insulation transformer 25 is to provide electrical insulatlon between the corona-proof housing 29 and the source of alternating potential 21..

It is not requisite of the invention'that alternating source of potential'lbe insulated by means of a transforn'ier, nor that the transformer be employed at all. It only happens that in the illustrated embodiment of this invention it is convenient, and the fact will be more fully pointed out and apparent upon the description of the contents of the corona-proof housing-'29.

The secondary 30, of insulation :trans--' former 25,supphes electrical 1 energy for transformer 31, which is preferably of a high reactance type, or it may be supplied with external resistance or reactance'32, to limit't-he short circuit current of the said transfori'ner.

Transforn'lor 31 is provided with-secondary 32 which, by means of leads33, supplies heating current for the cathode tube 18. 1 Transformer 31 isprovided with a tertiary winding 35, which is shunted by an;

adjustable critical voltage br alrdown-device 36,such as a spark-gap, or the like.

The said tertiary winning isfurthersh'unted by a condenser 37. The tertiary windin 35 saark- 'a 36 and the condenser 37 constitute a divided circuit 'for negative current passing fromrect1fier terminal .15

through lead20; thence dividied through these aforesaid three-circuits and to cathode 3e.

The'function of the high-resistor39 is that it serves to assist in the building up of the voltage across spark-gap 36, to cause of X-ray synchronous sparkbver' therebetweenj due to current flow from lead to the cathode of theX-ray tube 18. 1 Thisforced flow of current through the tertiary winding of transformer 31 is such that the variation in magnetic flux due thereto does not seriously affect the voltage of secondary'32, or said variation may be made to raise or lower said voltage somewhat without interfering materially with the operation of mydevice;

The condenser 37 is not an essential element of my invention, but 1n some cases 1mproves the operation thereof;

In the functioning ofmy device the operation is asfollows:

Alternating source of potential '1, set into operation, switch 28 is closed. Potential is induced into secondary of transformer at its proper speed, phaserelation and.

25, which in turn excites transformer 31, which in turn supplies potential forsecondary 32, which supplies the heatingcurrent to cathode 34 of X-ray tube 18. The X-ray tube 18 thus is supplied with thermionic electron-conductivity. Switch 24 is closed,

which sets synchronous moto'r21 into opera tion, which" motor being mechanically connected'to rectifier 13 drives the said rectifier polarity. The rectifier isthen in readiness to produce high-tension"direct current for theiX-ray tube 18. I 'Adju'stment 6 oftransformer .5 is selected to 'giv'e'the proper potential insecondary 8; switch 7 is closed. Direct current terminals 14 and 15'o'f rectifier 13 are then supplied which has not been so far described. This spark-over ofgap. 36 short-circuits the tertiary winding 35, whichreduces the magnetic induction in the core of the transformer 31, because of the high reactance characteristics of the primary circuit heretofore described. Thus the voltage. of secondary 32 is reduced and hence. the excitation current filament 34.

It will be appreciated'by those familiar with the art that this is a cyclic process and c this spark-over occurs during each half cycle 7 of the alternating current exciting the 5184- ment 34. That is, as each half lobe of the alternatingcurrent through filament 34 begins to buildup in value, it is only allowed to continue to flow according to its normal sinusoidal law until the discharge current through the tube has risen to thepredeter mined value, causing spark-over at 36', so that the filament exciting current is choked off, so to speak, during each half cycle when the discharge current through the X-ray tubehas' reached its predeterminedvalue.

This definite reductionof excitation current produces-the current limitation characteristic heretofore' referred to and thus serves as a stabilizenas will be more fully gone into. i a1: 1 The condenser 37 has the propertyof im proving the operation of the device by the a fact that the voltage-across the condenser is instantaneously proportional to the i11 tegrated value; of the current induced through it," or in other words, the'inst'an taneous. voltage which would influence spark-over of gap 36, is proportional to the quantity of current which 'ispa'ssed'. Theretore the spark-overcharacteristics of gap 36 and hence the "currentlimitat'ion characteristics of my device, as a whole, maybe [directedtowardthe limitation of the current flow from a quantitative standpoint'rather than instantaneous value, which would 'be the operating characteristic of my invention in-the absence ofthe condenser '37;

With the application-of potential-from rectifier-13 to the terminals of. X-ray tube 18, the conductivity ofth'esaid' tube as fixed,

by the current limitation characteristics of the cathode heating-current circuits just described, will be fixed independently" of whether the temperature'ofthe cathode 34 changes inherent-ly,' whether the gaseous ionization introduces a disturbing-factor, or the specific emission of the filament material changes, or the spontaneous ionization of the tube comes into play as a factor in conductivity, because. the thermionic emission of the cathode 34 is saliently the predominating factor in the conductivity of the said tube and sufiicient latitude is therefore at- ,forded thereby to hold the aggregate electron emission constant by" the adjustment of (this one factor, namely; the thermionic emis-' sion.

I It Will be appreciated by those skilled inthe art to which my invention appertains that various modifications of my invention may be made withoutdeparting from. the spirit of my invention such as for example, the use of my device-without rectifier 13 and with afdifferent type of X-ray tube and connection with various apparatus such as iscommon in the art or which may de velop in the future What I claim is: I 1. The combination of. an X ray tube having. main electrodes including a thermi onic cathode, a main circuit for supplying main energy 111 cycllc form to said electrodes, an independent circuit lncluding a limited-capacity transformer for supplying" having =rn ain electrodes including a rthermionic cathode, a niain-circuit for supplying mainge-nergy :in cyclic :Eorm to said electrodes, an independent circuit 'includingga limited-capacity .transfor ner for supplying heating current-for said cathode, and a translating device in the main energy circuit having a :negativewesistarme characteristic andoperatively associated yvith v -said transformer, whereby an increase. of current in themain circuit causes anincrease of loading upon said t-ransformer, thereby limiting ,the heat ing current per cycle for s d c hode- 3. The combination of an tube having main electrodes including a thermionic cathode, ,an ain circuit :i'or supplying main-energy in cyclic form to said electrodes, an independent circuit including a ll-HIltGd CRPQOltY l]If2H1SfOI'II1GI -i'or supply ng heating current to said cathode, and a means common to both main energy circuit and circuit of said transformer comprising a negative-resistance-characteristic -,load, whereby the increase oit'vcurrent in the main circuit causes an increase of loading upon said heating current for .sa-id cathode, and ;a

translating device in the main ,energy circult having an abruptfresistancebreakdowncharacteristic and operatively associated with said transformenavhereby the resistance. of the said device breaksdown abrupty each Cycle henepredet rmin am un of ,main-circuit energy fiows, causing additional load upon said transformer, thereby limiting the heatingcurrent per cycle for said cathode.

5. The combination 40f an 'Xmay tube having lnain =electrodes including a :thermionic cathode, .a main circuit for supplying main-energy in cyclic form to said electrodes, an independent circuit including ,a limited-capacity transformer for supplying heating, current for said cathode, ,and nea'ns in ,the main energy. circuit, operativelyassociated With said transformer, for causing ,an abrupt vresistance -,bre'akdovv'n characteristic load upon ,said nsformer, whereby the resistance ,of f the said means ,breaks down abruptly each a cycle avhen 1 predetermined amount of main-circuit energy fiows,.caus

ing additional load upon .saidtransto-rmer, thereby limiting the heating current per cycle for said'cathode. i ,In Witness whereof, I:l1ave 1.hereunto. set my .hand tl'llS10tlld21y of lanuary,l92l.- MONTFQRD .MQRRISON. 

